a(n) = 3*a(n-1) + a(n-2) - a(n-3) - a(n-5).

Terms

a(0) =4a(1) =13a(2) =42a(3) =135a(4) =433a(5) =1388a(6) =4449a(7) =14260a(8) =45706a(9) =146496a(10) =469546a(11) =1504979a(12) =4823727a(13) =15460908a(14) =49554976a(15) =158832563a(16) =509086778a(17) =1631714194a(18) =5229935889a(19) =16762880107a(20) =53728029453a(21) =172207945799a(22) =551957272549